selftests: rtnetlink.sh: remove esp4_offload after test

The esp4_offload module, loaded during IPsec offload tests, should
be reset to its default settings after testing.
Otherwise, leaving it enabled could unintentionally affect subsequence
test cases by keeping offload active.

Without this fix:
$ lsmod | grep offload; ./rtnetlink.sh -t kci_test_ipsec_offload ; lsmod | grep offload;
PASS: ipsec_offload
esp4_offload           12288  0
esp4                   32768  1 esp4_offload

With this fix:
$ lsmod | grep offload; ./rtnetlink.sh -t kci_test_ipsec_offload ; lsmod | grep offload;
PASS: ipsec_offload

Fixes: 2766a111 ("selftests: rtnetlink: add ipsec offload API test")
Signed-off-by: Xiumei Mu <xmu@redhat.com>
Reviewed-by: Shannon Nelson <sln@onemain.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/6d3a1d777c4de4eb0ca94ced9e77be8d48c5b12f.1753415428.git.xmu@redhat.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>